It depends on what (where) you want them for.
The biggest advantage of smart in-wall switches over smart bulbs is the way that the switch works with both the light and the ST hub. If you turn on or off the physical smart switch, you can turn it back on or off with ST. (And if you turn it on/off from ST, you can still turn it on/off from the physical switch.) As well, the smart switch still functions like a normal switch even when ST isn’t working.
With smart bulbs, if you turn off the bulb from a fixture or switch, the bulb is disconnected from the ST “network.” That means that ST can’t turn it back on. In fact, ST can’t even find the state of the bulb, so it’s almost as if you just completely unscrewed the bulb. In other words, for things to “work” properly, you can ONLY use ST to change the bulb status.
For these reasons, most people prefer using smart switches… if the light is usually controlled by a switch.
However, bulbs do have a few advantages over switches. For one, they are often less expensive than switches. As of this post, a “smart bulb” from Cree or GE (with dimming ability) costs about $15. A simple in-wall on/off smart switch costs at least double that. As well, the in-wall switch requires a bit of electrical wiring work, while a bulb only takes (insert bulb changing joke here) people to change it.